Substrate processing apparatuses have been used in recent years to perform various kinds of processing on substrates such as semiconductor wafers. One example of substrate processing apparatuses is a CMP (Chemical Mechanical Polishing) apparatus for polishing substrates.
The CMP apparatus includes a polishing unit for polishing substrates, a cleaning unit for cleaning and drying the substrates, a loading/unloading unit that delivers the substrates to the polishing unit and receives the substrates cleaned and dried by the cleaning unit, etc. The CMP apparatus further includes a transfer unit that transfers the substrates among the polishing, cleaning, and loading/unloading units. The CMP apparatus transfers the substrates by means of the transfer unit, and serially performs the various kinds of processing, including polishing, cleaning, and drying.
The polishing unit includes a polishing table to which a polishing pad for polishing a substrate is attached, and a holding portion for holding and pressing the substrate against the polishing pad. Inside the holding portion, there are provided a plurality of airbags for holding the substrate while sucking the substrate onto the holding portion and pressing the substrate against the polishing pad. The use of the airbags enables the entire substrate to be applied with uniform pressure, thereby achieving a uniform and stable polishing characteristic. To that end, the pressure applied to the airbags is previously calibrated (corrected) to have a predetermined value with accuracy.
According to conventional calibration methods, an airbag conduit located near an airbag membrane is pulled out and connected to a pressure gauge. In accordance with a value measured at the pressure gauge, a D/A parameter for calibration is calibrated. Specifically, with respect to an initial parameter, measured values obtained when a plurality of specified pressures are applied are recorded. A post-calibration parameter is then calculated from the measured values by using a calculation formula, and reflected in the apparatus. After the post-calibration parameter is reflected, measured values of pressure are checked again. If the measured values are out of a required accuracy range, the post-calibration parameter is recalculated and reflected in the apparatus. The above-described process is repeated until the specified accuracy is satisfied. The process is performed on a single airbag and therefore needs to be carried out with respect to each polishing table and airbag of the apparatus. Further, the calibration includes two operations, namely, an operation including operating the apparatus and changing the parameter, and an operation including measurement of pressure and calculation. In this light, the calibration is carried out preferably by two persons for efficiency's sake.